Method for preparing branched polycarbonate with continuous two-phase interface phosgene method

Abstract

The present invention relates to a method for preparing branched polycarbonate with a continuous two-phase interface phosgene method. Firstly, an aqueous solution of alkali metal hydroxide with triphenol and polyphenol dissolved therein reacts with a certain amount of phosgene in the present of inert organic solvent to prepare a prepolymer, and then a coupling reaction is performed among the prepolymer, an aqueous solution of alkali metal hydroxide with bisphenol and phosgene dissolved therein to finally obtain a polycarbonate resin. The method can avoid a cross-linking reaction, reduce the cost and improve the quality of the product, while improving the conversion ratio of the branching agent and the branching degree of the product.

The invention claimed is: 
     
       1. A method for preparing a branched polycarbonate via a continuous two-phase phosgenation interfacial process, comprising the steps of:
 a) dissolving a branching agent into an aqueous solution of alkali metal hydroxide to form a first aqueous phase, then conducting a pre-reaction between the first aqueous phase and phosgene in the existence of an inert organic solvent to prepare a prepolymer; wherein the mole ratio of the phosgene to the phenolic hydroxyl group of the branching agent is from 0.1:1 to 2:1; 
 b) dissolving a bisphenol into an aqueous solution of alkali metal hydroxide to form a second aqueous phase, then conducting a reaction among the prepolymer prepared by step a), the second aqueous phase and phosgene in the existence of an inert organic solvent to prepare a branched polycarbonate oligomer; and 
 c) adding an end capping agent and a catalyst into the oligomer prepared by step b) to carry out the chain extension and end capping reaction to obtain a solution of a high molecular weight branched polycarbonate, and finally obtaining the branched polycarbonate by separating and purifying. 
 
     
     
       2. The method according to  claim 1 , in the pre-reaction of step a), the pH value of the first aqueous phase is maintained in the range of 12 to 14. 
     
     
       3. The method according to  claim 1 , wherein, a residence time of the pre-reaction of step a) is in the range of 0.1 s to 10 s. 
     
     
       4. The method according to  claim 1 , in the pre-reaction of step a), the reaction temperature is below 40° C. 
     
     
       5. The method according to  claim 1 , wherein the branching agent of step a) is a compound comprising three or more phenolic hydroxyl groups, or the combination thereof; and the concentration of the branching agent in the first aqueous phase is from 3 wt % to 25 wt %. 
     
     
       6. The method according to  claim 1 , in the reaction of step b), the pH value of the second aqueous phase is maintained in the range of 10 to 13. 
     
     
       7. The method according to  claim 1 , wherein a residence time of the reaction of step b) is in the range of 1 s to 20 mins. 
     
     
       8. The method according to  claim 1 , in step b), the bisphenol is bisphenol A or tetrabromo bisphenol A; the concentration of the bisphenol in the second aqueous phase is from 5 wt % to 25 wt %. 
     
     
       9. The method according to  claim 1 , wherein the total mole amount of the phosgene in steps a) and b) is in the range of 1.03 times to 1.2 times of the sum of the mole amounts of the branching agent and the bisphenol. 
     
     
       10. The method according to  claim 1 , wherein the mole percentage of the branching agent in step a) is in the range of 0.1% to 2% of the mole percentage of the bisphenol in step b). 
     
     
       11. The method according to  claim 1 , in steps a) and b), the inert organic solvent can be one or more of dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, toluene, chlorobenzene or carbon tetrachloride; and the concentration of the phosgene in the inert organic solvent is from 3 wt % to 20 wt %. 
     
     
       12. The method according to  claim 1 , wherein in the pre-reaction of step a), the mole ratio of the phosgene to the phenolic hydroxyl group of the branching agent is from 0.25:1 to 1:1. 
     
     
       13. The method according to  claim 2 , wherein in the pre-reaction of step a), the pH value of the first aqueous phase is maintained in the range of 12.8 to 13.5. 
     
     
       14. The method according to  claim 3 , wherein the residence time of the pre-reaction of step a) is in the range of 0.5 s to 2 s. 
     
     
       15. The method according to  claim 5 , wherein the branching agent of step a) is one or more of 1,1,1-tri(4-hydroxyphenyl)ethane, 1,3,5-trihydroxybenzene, 1,2,3-trihydroxybenzene, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptane, 1,1,2,2-tetra(4-hydroxyphenyl)ethane, 1,1,3,3-tetra(4-hydroxyphenyl)propane, 2,2,4,4,-tetra(4-hydroxyphenyl)pentane, 2,2,5,5-tetra(4-hydroxyphenyl)hexane or 1,1,2,2,-tetra(3-methyl-4-hydroxyphenyl)ethane; and the concentration of the branching agent in the first aqueous phase is from 8 wt % to 20 wt %. 
     
     
       16. The method according to  claim 15 , wherein the branching agent of step a) is 1,1,1-tri(4-hydroxyphenyl)ethane. 
     
     
       17. The method according to  claim 6 , wherein in the reaction of step b), the pH value of the second aqueous phase is maintained in the range of 12 to 12.8. 
     
     
       18. The method according to  claim 7 , wherein the residence time of the reaction of step b) is in the range of 1 s to 5 mins. 
     
     
       19. The method according to  claim 9 , wherein the total mole amount of the phosgene in steps a) and b) is in the range of 1.05 times to 1.12 times of the sum of the mole amounts of the branching agent and the bisphenol. 
     
     
       20. The method according to  claim 10 , wherein the mole percentage of the branching agent in step a) is in the range of 0.2% to 0.8% of the mole percentage of the bisphenol in step b).